A conventional hair trimmer 60 is disclosed in FIGS. 7 and 8, and generally includes a body with a handle and a blade connection portion 62. A finger ring 61 is connected to a distal end of the handle and a recess 64 is defined in a side of the blade connection portion 62. Two positioning protrusions 63 extend from an inside of the recess 64 so that two holes 72 of a blade 70 are mounted onto the positioning protrusions 63. The blade 70 is then positioned in the recess 64 and includes an edge 71 which is exposed beyond a lower edge of the blade connection portion 62. A block 80 has one end with a boss 81 which is pivotably engaged with a notch 65 defined in the inside of the recess 64 so that the block 80 is pivoted to cover the blade 70 and the edge 71 is exposed beyond the lower edge 800 of the block 80 to proceed trimming. An engaging recess 82 is defined in the other end of the block 80 such that when the block 80 is pivoted to cover the blade 70, the engaging recess 82 is engaged with a cooperation portion in the recess 64 to position the block 80. Although the blocks 80 can be replaced so as to have different shapes of lower edges 800, the user might be cut by the edge 71 of the blade 70 when pivoting the block 80.
The present invention intends to provide a trimmer that uses a clamp to hold the pattern block from a top of the blade connection portion to avoid the shortcoming mentioned above.